Initially, all or mostly all Altcoins will follow and drop in value. I think if the cause for the drop involves regulation on bitcoin, hodlers of bitcoin will start selling and possibly start buying into alts with 'stealth/privacy' features, causing* those specific coin/token values to rise again.

What I find interesting is the idea of banning all 'cryptocurrencies'.  I do not think that would not work. Many businesses have adopted the gen1 and gen2 cyptocurrencies into their business plan and product/services lines.  See Deloitte, American express, Monster Technologies, IBM stellar, and the list can go on. If you know of others, send me a PM and educate me please  

Regulation is the most probable in my opinion.